1. Field of the Invention
The present invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) method, and more particularly to a sub-carrier allocation method for reducing inter-cell interference in an OFDM cellular environment.
2. Background of the Related Art
Current mobile communication standardization technologies include an AMPS (Advanced Mobile Phone system) and WCDMA (Wideband Code Division Multiple Access) system. In these communication systems, multiplexing is used to support multiple users by constructing multiple communication paths (channels) to transmit and receive an independent signal. In more detail, multiplexing divides one line or transmission path in to multiple channels (for a fixed line, a pair of cables, and for a wireless service, a pair of transceivers).
Examples of multiplexing methods include a FDM (Frequency Division Multiplexing) method in which one line is divided into multiple frequency bands and then multiplexed, and a TDM (Time Division Multiplexing) method in which one line is divided into very short time intervals and then multiplexed.
AMPS, which is a first generation analog mobile communication standard, uses FDM. A second generation mobile communication system is called IS-95, and uses a CDM (Code Division Multiplexing) method. A third generation mobile communication system is called WCDMA (Wideband Code Division Multiple Access) and uses a Code Division Multiplexing (CDM) method.
Another type of multiplexing is called the Orthogonal Frequency Division Multiplexing (OFDM). OFDM is based on a principle of multicarrier modulation, which means dividing a data stream into several bit streams (subchannels), each of which has a much lower bit rate than the parent data stream. These substreams are then modulated using frequencies that are orthogonal to each other. Because of their orthogonality, the subcarriers can be very close to each other (or even partly overlapping) in the frequency spectrum without interfering with each other. Further, because the symbol times on these low bit rate channels are long, there is generally no intersymbol interference (ISI). The result is a very spectrum efficient system.
Digital Audio Broadcasting (DAB) and Digital Video Broadcasting (DVB) are based on OFDM. However, OFDM is not used in a cellular communication system including multiple cells.